Organic EL display device

ABSTRACT

In an organic EL display device comprising a substrate, a plurality of pixel regions in each of which a first electrode, a light emitting material layer, and a second electrode are laminated in this order above the substrate, and a bank film formed above the substrate to separate respective one of the pixel regions from another of the pixel regions adjacent thereto, wherein the bank film has a plurality of openings exposing upper surfaces of the first electrodes to the light emitting material layers in the respective pixel regions, and the second electrode is formed over the a plurality of openings of the bank film in common with the pixel regions, the present invention forms the bank film of an inorganic material and shapes a side wall thereof lying around each of the openings thereof to be sloped at an angle less than 85 degrees (°) with respect to a principal surface of the substrate in order to prevent the deterioration of the light emitting material layer and disconnection of the second electrode at steps of bank film lying in the vicinity of the openings thereof.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of application Ser. No.10/732,278, filed Dec. 11, 2003 now U.S. Pat. No. 7,034,453, thedisclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic EL (Electro-Luminescence)display device.

2. Description of the Related Art

An organic EL display device is constituted such that on each pixelregion of a substrate, at least one electrode (for example an anode), alight emitting material layer (or a plurality of organic material layersincluding the light emitting material layer) and another electrode (forexample, a cathode) are formed in a laminated manner. A plurality ofthese pixel regions are arranged two-dimensionally on the substrate soas to form a display region (an effective display region) which displaysimages. In each of a plurality of pixel regions, one of a pair ofelectrodes (for example, the above-mentioned anode and cathode) whichsandwich the light emitting material layer may be formed as a commonelectrode which spreads over a plurality of pixel regions.

In each of the above-mentioned pixel regions, due to an electric currentwhich flows form one of the pair of electrodes which sandwich the lightemitting material layer to another of the pair of electrodes through thelight emitting material layer, the light emitting material layer is madeto emit light and hence, an image is displayed on the display region.

In the organic EL display device, the light emitting material layer isformed of organic material and hence, the light emitting material layeris liable to suffer from the degradation due to moisture or the like.Accordingly, in forming the light emitting material layer, a selectiveetching method based on a photolithography technique cannot be used. Ina manufacturing process of the organic EL display device having thelight emitting material layer made of low-molecular-system organicmaterial, in place of the selective etching method, for example, using avapor deposition shadow mask, light emitting material (organic material)which is vaporized by sublimation or the like is selectively adhered togiven positions thus forming (sublimating) a light emitting materiallayer in a given pattern.

In the manufacturing step of the organic EL display device, a selectiveetching method which uses an etchant after forming the light emittingmaterial layer cannot be utilized and hence, it is necessary to providea structural body which insulates a pair of laminated electrodes at bothsides of the light emitting material layer in the pixel region beforeforming the light emitting material layer. To cope with such a request,there has been known a technique in which an insulation film (a bankfilm) in which a recessed portion is formed is preliminarily formed atportions where the light emitting material layer is formed.

In this case, one electrode (hereinafter referred to as pixel electrode)is formed as a layer below the light emitting material layer and anotherelectrode (hereinafter referred to as a counter electrode) is commonlyformed on respective pixel regions and hence, the counter electrode isusually formed such that the counter electrode covers the light emittingmaterial layer and the surface of the bank film (see Japanese UnexaminedPatent Publication Hei11(1999)-329741).

Conventionally, as the bank film, an organic material layer (forexample, made of resin) which can be easily formed is generally used.The bank film made of the organic material is formed with a thickness(layer thickness) of approximately 1 μm. On the other hand, a methodwhich forms the bank film using the inorganic material has been proposed(see Japanese Unexamined Patent Publication 2001-68267).

SUMMARY OF THE INVENTION

However, in the organic EL display device (also referred to as OrganicElectroluminescent Display Device or OLED (Organic Light-Emitting Diode)Display) having the bank film made of organic material, a non-lightemitting region has often appeared at an end portion of the pixel.

Inventors of the present invention have pursued a cause of thisphenomenon and have found that moisture, oxygen or the like contained inthe bank film made of organic material is relevant to theabove-mentioned degradation of pixels (the occurrence ofnon-light-emitting region). When the bank film made of the organicmaterial has an interface which comes into contact with a light emittingmaterial layer (an organic material layer which exhibits anelectroluminescence phenomenon), moisture, oxygen and the like containedin the bank film are diffused into the light emitting material layerfrom the interface. The light emitting material layer (organic materiallayer), due to the unexpected diffusion of moisture, oxygen and the likein the inside thereof, inevitably receives the change of electron stateand loses desirable electric field light-emitting characteristics.

Since the degradation of the light emitting material layer is remarkablein the vicinity of the interface with the bank film where a diffusionquantity of moisture, oxygen and the like is large, the above-mentionednon-light-emitting region (also referred to as the non-light-emittingportion or the dark spot) is formed at an end portion of the pixel (thelight emitting region formed of the above-mentioned organic material)which is brought into contact with the bank film. With respect to such adrawback, it is unavoidable that any organic material which is used asthe bank material contains approximately 0.1% of water content.Accordingly, so long as the bank film is formed of the organic material,it is difficult to prevent the occurrence of the non-light-emittingregion at the end portion of the pixel which constitutes the organic ELelement. Further, even when an electron-transporting layer or ahole-transporting layer is formed between the bank film and the lightemitting material layer, this does not solve this drawback.

On the other hand, the bank film made of inorganic material exhibits anextremely small quantity of moisture, oxygen or the like contained inthe bank film compared to the bank film made of the organic material andhence, such a bank film is considered to be preferable to suppress theoccurrence of the above-mentioned non-light emitting region at the endportion of the pixel. However, the inventors of the present inventionhave also found the occurrence of the non-light emitting region at theend portion of the pixel even with respect to the organic EL displaydevice having the bank film formed of the inorganic material. Theinventors have focused their attention on a shape of the bank film as acause which generates such a drawback even with respect to the organicEL display device provided with the bank film made of inorganicmaterial.

The bank film made of the organic material has a so-called trapezoidalcross section in which side walls of the bank film make an inclined facewith respect to a background layer thereof or a principal surface of thesubstrate on which the background layer or an EL array(Electroluminescent Array) is formed. An angle with which the side wallsof the bank film which are inclined make with respect to the backgroundlayer or the principal surface of the substrate (hereinafter referred toas a taper angle) is in a range of 30 to 70 degrees. Accordingly, thelight emitting material layer and the counter electrode are notdisconnected at a stepped portion between the end portion of the bankfilm or an upper surface of the pixel electrode and an upper surface ofthe bank film. That is, the light emitting material layer and thecounter electrode are stacked such that they extend from an uppersurface of the pixel electrode to an upper surface of the bank filmalong the inclined surfaces of the bank film.

On the other hand, the side walls of the bank film made of inorganicmaterial erect at an angle of approximately 90 degrees with respect tothe background layer (or the principal surface of the substrate).Accordingly, due to a steep stepped portion which is formed between theupper surface of the pixel electrode and the upper surface of the bankfilm, the light-emitting material layer or the counter electrode(conductive layer) which extends from the upper surface of the pixelelectrode to the upper surface of the bank film becomes thin or isdisconnected at an end portion (a portion where these layers get overthe stepped portion) of the pixel. In other words, the light emittingmaterial layer or the counter electrode is not sufficiently stacked onthe end portion of the bank film which is formed like an upright wall. Adefect in the layer (film) formation at the stepped portion is alsoreferred to as film thickness loss, stepped disconnection or a stepfault.

When the light emitting material layer is stacked from the upper surfaceof the pixel electrode to the upper surface of the bank film formed onthe end portion of the pixel electrode and, thereafter, the counterelectrode layer (conductive layer) is stacked to cover the lightemitting material layer, the above-mentioned film thickness loss or stepdisconnection occurs in the light emitting material layer at the steppedportion between the bank film and the pixel electrode which is formed asascending abruptly from the upper surface of the pixel electrode. Whenthe conductive layer which constitutes the counter electrode is stackedon the light emitting material layer having such an incomplete shape,the film thickness loss or the step disconnection occurs also withrespect to the counter electrode. Accordingly, at a stage that an ELarray (a pixel array of the display device) is completed on theprincipal surface of the substrate, the light emitting material layer isnot sufficiently covered with the counter electrode and hence, moisture,oxygen and the like which are contained in the atmosphere of thesubstrate of the EL array intrude and diffuse into the light emittingmaterial layer through the film thickness loss portion or the stepdisconnection portion which are formed in the counter electrode. As aresult, in the same manner as the organic EL display device having thebank film made of the organic material, the non-light-emitting region isformed at the end portion of the pixel (portion where the stepdisconnection of the counter electrode occurs) even with respect to theorganic EL display device having the bank film made of inorganicmaterial.

Further, there exists a possibility that the film thickness loss or thestep disconnection which occurs in the light emitting material layermakes the pixel electrode and the counter electrode which are to bespaced apart by the light emitting material layer come abnormally closeto each other thus bringing them into a short-circuit. Accordingly,there also exists a possibility that an electric field is concentratedon the end portion of the pixel thus generating leaking of an electriccurrent. In an extreme case, there exists a possibility that a cavity isformed in the light emitting material layer or the light emittingmaterial layer is carbonized due to Joule heat generated by suchconcentration of electric field strength or leaking of an electriccurrent.

The present invention has been made in view of the above-mentionedcircumstances and it is an object of the present invention to provide anorganic EL display device which suppresses the degradation of the lightemitting region which is attributed to a bank film and, at the sametime, can suppress the failure in formation of a counter electrode and alight emitting material layer and the failure in image display.

To briefly explain the summary of representative inventions among theinventions disclosed in this specification, they are as follows.

Means 1

One of exemplified organic EL display devices according to the presentinvention (the means 1) comprising:

-   (1) a substrate;-   (2) a plurality of pixel regions each of which has at least a first    electrode, a light emitting material layer, and a second electrode    laminated in this order above a principal surface of the substrate,    the plurality of pixel regions are arranged two-dimensionally in the    principal surface of the substrate; and-   (3) a bank film formed above the principal surface of the substrate    to separate respective one of the plurality of pixel regions from    another of the plurality of pixel regions adjacent to the respective    one of the plurality of pixel regions, the bank film has openings    each of which exposes the first electrode provided for the    respective one of the plurality of pixel regions,

wherein

-   (4) the light emitting material layer is formed in the opening of    the bank film to be extended to a side wall of the bank film lying    along the opening in the respective one of the plurality of pixel    regions,-   (5) the second electrode provided for the respective one of the    plurality of pixel regions is formed in common with that provided    for the another of the plurality of pixel regions, and-   (6) the bank film is constituted of at least one inorganic material    layer and has the side wall thereof sloped at an angle less than 85    degrees (°) with respect to the principal surface of the substrate.

The slope angle less than 85 degrees of the side wall of the bank filmmay also defined with respect to an upper surface of the first electrodein contact with the bank film instead of the principal surface of thesubstrate as defined the item (6) described above.

Means 2

Another of exemplified organic EL display devices according to thepresent invention (the means 2) comprising:

-   (1) a substrate; and-   (7) a plurality of pixel regions arranged in a principal surface of    the substrate, respective one of the plurality of pixel regions has    a first electrode, a bank film, a light emitting material layer, and    a second electrode stacked in this order above the principal surface    of the substrate,

wherein

-   (8) the bank film spaces the first electrode provided for the    respective one of the plurality of pixel regions from that provided    for another of the plurality of pixel regions adjacent to the    respective one of the plurality of pixel regions,-   (9) the second electrode is formed in common with the plurality of    pixel regions,-   (10) the bank film has an opening exposing a part of an upper    surface of the first electrode toward the light emitting material    layer and a side wall located along the opening,-   (11) the light emitting material layer is formed in the opening of    the bank film and in the vicinity thereof, and-   (6) the bank film is constituted of at least one inorganic material    layer and has the side wall thereof inclined at an angle less than    85 degrees (°) with respect to the principal surface of the    substrate.

The inclination angle less than 85 degrees of the side wall of the bankfilm may also defined with respect to an upper surface of the firstelectrode in contact with the bank film instead of the principal surfaceof the substrate as defined the item (6) described above.

Means 3

In an organic EL display devices according to the present inventionincluding the constitution defined by the means 2, the light emittingmaterial layer provided for the respective one of the plurality of pixelregions is overlapped with the other light emitting material providedfor the another of the plurality of pixel regions on a surface of thebank film. If one of the plurality of pixel regions and another thereofadjacent to the one thereof radiate light having the same color, thelight emitting material layer may be formed in common with the onethereof and the another thereof by extending the light emitting materiallayer from the one thereof to the another thereof.

Means 4

In an organic EL display devices according to the present inventionincluding the constitution defined by either one of the means 1, themeans 2, and the means 3, the bank film is formed of a silicon nitridefilm (SiN_(x)).

Means 5

In an organic EL display devices according to the present inventionincluding the constitution defined by the means 4, a composition ratioof nitrogen x of the silicon nitride film (SiN_(x)) is different betweena lower side of the silicon nitride film located closer to the principalsurface of the substrate and an upper side thereof further from theprincipal surface of the substrate opposed to the lower side thereof todecrease an etching rate thereof at the lower side thereof in comparisonwith that at the upper side thereof.

Instead of the means 5 described above, the silicon nitride film mayformed of a plurality of layers laminated above the principal surface ofthe substrate, so that composition ratio of nitrogen x in the pluralityof layers is different from each other to decrease an etching rate ofthe silicon nitride film as closer to the principal surface of thesubstrate in an organic EL display devices according to the presentinvention including the constitution defined by the means 4.

Means 6

In an organic EL display devices according to the present inventionincluding the constitution defined by either one of the means 1 and themeans 2, the side wall of the bank film is shaped into a curvatureextended from an upper surface of the first electrode to an uppersurface of the bank film.

Means 7

In an organic EL display devices according to the present inventionincluding the constitution defined by either one of the means 1, themeans 2, and the means 6, the side wall of the bank film is partiallysloped at an angle not less than 85 degrees with respect to theprincipal surface of the substrate between an upper surface of the firstelectrode to an upper surface of the bank film. In other words, the sidewall of the bank film may meet the principal surface of the substrate atan angle equal to or greater than 85 degrees (°) partially as long as apart thereof meets the principal surface of the substrate at an angleless than 85 degrees. In the organic EL display devices including theconstitution defined by the means 6, a tangent or a tangent planecontacting a part of the curvature (the side wall of the bank film) maymeet the principal surface of the substrate at an angle equal to orgreater than 85 degrees on condition that another tangent or anothertangent plane contacting another part of the curvature (other than thepart thereof) meets the principal surface of the substrate at an angleless than 85 degrees. The principal surface of the substrate meetingeither one of the side wall of the bank film, the tangent in contacttherewith, and the tangent plane in contact therewith may be replacedwith an upper surface of the first electrode in contact with the bankfilm.

Means 8

In an organic EL display devices according to the present inventioncomprising a plurality of gate signal lines and a plurality of drainsignal lines both formed on the principal surface of the substrate aswell as the constitution defined by either one of the means 1 and themeans 2,

the respective one of plurality of pixel regions has a switching elementwhich receives a video signal from one of the plurality of drain signallines while the switching element is turned on by a scanning signaltransmitted by one of the plurality of gate signal lines, and

a current in accordance with the video signal flows between the firstelectrode and the second electrode through the light emitting materiallayer in the respective one of plurality of pixel regions.

Means 9

In an organic EL display devices according to the present inventionincluding the constitution defined by the means 8, the second electrodeis formed also over an upper surface of the bank film in common with theplurality of pixel regions, and a reference signal to the video signalis supplied to the second electrode.

Here, the present inventions are not limited to the above-mentionedconstitutions and various modifications are conceivable withoutdeparting from the technical concept of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing one embodiment of a pixel of anorganic EL display device according to the present invention and also isa cross-sectional view taken along a line I-I in FIG. 3;

FIG. 2 is an equivalent circuit diagram showing one embodiment of adisplay part of an organic EL display device according to the presentinvention;

FIG. 3 is a plan view showing one embodiment of a pixel of an organic ELdisplay device according to the present invention;

FIG. 4 is a cross-sectional view taken along a line IV-IV in FIG. 3;

FIG. 5A to FIG. 5C are explanatory views showing an advantageous effectof the organic EL display device according to the present invention;

FIG. 6 is a cross-sectional view showing one embodiment of amanufacturing method of the organic EL display device according to thepresent invention;

FIG. 7A to FIG. 7C are cross-sectional views of another embodiments ofthe pixel of the organic EL display device according to the presentinvention; and

FIG. 8A to FIG. 8D are cross-sectional views of another embodiments ofthe pixel of the organic EL display device according to the presentinvention.

DETAILED DESCRIPTION

Embodiments of an organic EL display device according to the presentinvention are explained in conjunction with the drawings.

Embodiment 1

<<Equivalent Circuit of the Display Part>>

FIG. 2 is an equivalent circuit diagram of one embodiment of the organicEL display device according to the present invention.

In the drawing, gate signal lines GL which extend in the x direction inthe drawing and are arranged in parallel in the y direction in thedrawing and drain signal lines DL which extend in the y direction in thedrawing and are arranged in parallel in the x direction in the drawingare formed.

Respective rectangular regions which are surrounded by these gate signallines GL and drain signal lines DL constitute pixel regions and a massof these pixel regions form a display region.

Each pixel region includes a thin film transistor TFT which is turned onin response to a scanning signal from the one-side (upper side in thedrawing) gate signal line GL and a pixel electrode PX to which a videosignal is supplied from the one-side (left side in the drawing) drainsignal line DL by way of the thin film transistor TFT. In acurrent-drive type organic EL display device which makes the pixel emitlight by re-coupling an electron and a hole in a light emitting materiallayer, the video signals are supplied as current signals. Further, acurrent supply line not shown in FIG. 2 may be formed on a substrate andthin film transistors for supplying a current which are controlled inresponse to video signals may be newly formed in respective pixelregions, and a given current may be supplied to pixel electrodes throughthe thin film transistors for supplying a current from the currentsupply line in response to a voltage of the video signal.

The pixel electrode PX is configured to sandwich a light emittingmaterial layer between the pixel electrode PX and a counter electrodenot shown in the drawing, and the light emitting material layer is madeto emit light in response to a current which flows between the pixelelectrode PX and the counter electrode.

Here, the counter electrode is formed commonly with respect torespective pixel regions and supplies a signal which becomes thereference with respect to the video signal.

In such a constitution, the display device is driven such that one ofrespective gate signal lines GL is selected one after another inresponse to the supply of the scanning signal, while the video signal issupplied to respective drain signal lines DL at the selection timing ofthe gate signal line GL.

<<Constitution of Pixel>>

FIG. 3 is a plan view showing one embodiment of the above-mentionedpixel. Further, a cross section taken along a line I-I in FIG. 3 isshown in FIG. 1 and a cross section taken along a line IV-IV in FIG. 3is shown in FIG. 4.

In FIG. 3, for example, at a left upper portion of each pixel region ona surface of the substrate SUB1 (see FIG. 1 and FIG. 4) made of glass,for example, a semiconductor layer PS formed of a polysilicon layerwhich extends in the x direction in the drawing is formed. Thesemiconductor layer PS constitutes a semiconductor layer of the thinfilm transistor TFT.

Then, an insulation film GI (see FIG. 1 and FIG. 4) is formed on thesurface of the substrate SUB1 such that the insulation film GI alsocovers the semiconductor layer PS. The insulation film GI functions as agate insulation film in a region where the thin film transistor TFT isformed.

On a surface of the insulation film GI, the gate signal lines GL whichextend in the x direction and are arranged in parallel in the ydirection are formed. The gate signal lines GL are formed such that thegate signal lines GL define the pixel regions together with the drainsignal lines DL explained later.

Further, an extending portion which extends such that a portion thereoftraverses a substantially center portion of the semiconductor layer PSis formed on the gate signal line GL. The extending portion functions asa gate electrode GT of the thin film transistor TFT.

Here, after formation of the gate electrode GT, impurity ions areinjected using the gate electrode GT as a mask so that portions of thesemiconductor layer PS in the regions other than a region immediatelybelow the gate electrode GT are made less resistant.

An insulation film IN (see FIG. 1, FIG. 4) is formed on the surface ofthe substrate SUB1 such that the insulation film IN also covers the gatesignal lines GL (gate electrodes GT). This insulation film IN functionsas an interlayer insulation film with respect to the gate signal line GLin the region for forming the drain signal line DL explained next.

On a surface of the insulation film IN, the drain signal lines DL whichextend in the y direction and are arranged in parallel in the xdirection are formed. A portion of the drain signal line DL extends toone end portion of the semiconductor layer PS and is connected to thesemiconductor layer PS via a through hole TH1 which is preliminarilyformed by penetrating the insulation film IN and the insulation film GI.That is, the extending portion of the drain signal line DL functions asa drain electrode SD1 of the thin film transistor TFT.

Further, in another end portion of the semiconductor layer PS, a sourceelectrode SD2 which is connected via a through hole TH2 which ispreliminarily formed by penetrating the insulation film IN and theinsulation film GI is formed. The source electrode SD2 is provided withan extending portion for connecting the source electrode SD2 with thepixel electrode PX described later.

Then, on a surface of the substrate SUB1 on which the drain signal linesDL (drain electrodes SD1) and source electrodes SD2 are formed in such amanner, an insulation film IL (see FIG. 1 and FIG. 4) is formed.

On an upper surface of the insulation film IL, the pixel (anode)electrode PX is formed at the center except for a trivial periphery ineach pixel region and the pixel electrode PX has a portion thereofconnected to the above-mentioned extending portion of the sourceelectrode SD2. Here, the pixel electrode PX is, for example, formed of alight transmitting conductive film such as ITO (Indium Tin Oxide). Thisprovision is made to allow light from the light emitting material layerFLR described later to pass through the pixel electrode PX toward thesubstrate SUB1 side.

On an upper surface of the pixel electrode PX, the light emittingmaterial layer FLR is formed. The light emitting material layer FLRcontains a fluorescent organic material which emits light by applying agiven voltage such as quinolinol complex, oxazole complex, various laserpigments, polyparaphenylene vinylene or the like.

Further, the light emitting material layer FLR may be formed, ifnecessary, by laminating a hole transporting layer which has a functionof efficiently transporting holes injected from the electrode to thelight emitting material layer or the like.

In this specification, even when the light emitting material layer FLRis formed by laminating a hole importing layer, an electron injectinglayer or the like besides the light emitting material layer, such acombination is also referred to as the light emitting material layer FLRin a form that the light emitting material layer FLR includes theselayers.

Here, although the light emitting material layer FLR is formed (filled)such that the light emitting material layer FLR is defined from otherneighboring light emitting material layer FLR by a bank (partition wall)film BNK, the light emitting material layer FLR is formed such that thelight emitting material layer FLR covers an opening portion (portionwhere the pixel electrode PX is exposed) in the bank film BNK, reaches aside wall portion of the bank film BNK and extends over a surfaceportion of the bank film BNK. In other words, the light emittingmaterial layer FLR is formed such that the light emitting material layerFLR covers the opening portion of the bank film BNK and, at the sametime, reaches the periphery of the opening portion.

This provision is made to preliminarily ensure the large tolerance tocope with the displacement of the mask (vapor deposition shadow mask) informing the light emitting material layer FLR. Accordingly, it ispossible to obtain an advantageous effect that alignment of the mask canbe easily performed.

Here, in this case, it is needless to say that the light emittingmaterial layer FLR of the pixel region and the light emitting materiallayer of the another pixel region which is disposed close to the pixelregion form a portion where they are superposed each other.

This is because that the tolerance against the mask displacement at thetime of forming the light emitting material layer FLR can be furtherincreased and hence, the distance between the pixels can be narrowedwhereby the display of high definition can be realized.

Here, the bank film BNK is formed of an inorganic material layer madeof, for example, SiNx, SiO₂ or the like and the side wall in the openingthereof is formed to have an inclination which flares toward the lightemitting material layer FLR side. Here, the inclination is set to lessthan 85 degrees, and more preferably, to 80 to 10 degrees. Advantageouseffects obtained by the material of the bank film BNK and theinclination of the side wall are explained in detail later.

A layer thickness of the light emitting material layer FLR is setthinner than a layer thickness of the bank film BNK and hence, the lightemitting material layer FLR is formed with a stepped portion at aposition of the side wall in the opening portion formed in the bank filmBNK.

On the upper surfaces of the light emitting material layer FLR and thebank film BNK, a counter (cathode) electrode CT which is used in commonby respective pixel regions is formed using aluminum or the like, forexample. In this case, the counter electrode CT is also formed with astepped portion at a position of the side wall in the opening portionformed in the bank film BNK.

Then, to an upper surface of the counter electrode CT, the substrateSUB2 made of glass, for example, is laminated by way of a high molecularresin seal PSL, for example.

By supplying an electric current to the light emitting material layerFLR interposed between the pixel electrode PX and the counter electrodeCT, the light emitting material layer FLR emits light and this light LTcan be observed with naked eyes through the pixel electrode PX and thesubstrate SUB1.

Here, a voltage signal which becomes the reference with respect to thevideo signal is applied to the counter electrode CT, while the videosignal is applied to the pixel electrode PX from the drain signal lineDL through the thin film transistor TFT. Further, the thin filmtransistor TFT is switched on in response to the scanning signal fromthe gate signal line GL.

<<Comparison of Shape and Material of Bank Film>>

As described above, with respect to the bank film BNK which defines thesubstantial pixel region, as shown in FIG. 5A, a side wall having agentle inclination is formed at the center side of the pixel region andhence, the light emitting material layer FLR and the counter electrodeCT which are formed thereafter can be formed respectively such that nostep disconnection is generated at respective side walls thereof.

FIG. 5B shows a cross section of a bank film BNK which is formed ofinorganic material and has a stepped portion close to 90 degrees. ThisFIG. 5B is also an explanatory view of one comparison example for thecross section of the bank film BNK of the present invention shown inFIG. 5A. A side wall of the bank film BNK shown in FIG. 5B erects at anangle (inclination angle) which is close to perpendicular with respectto a surface of the pixel electrode PX (background layer of the bankfilm BNK) and hence, it is difficult to stack the light emittingmaterial layer FLR on the side wall whereby the disconnection portion(step disconnection) of the light emitting material layer FLR isgenerated in a valley shape at an end portion of the bank film BNK. Suchstep disconnection of the light emitting material layer FLR is succeededby the shape of the counter electrode CT formed on the upper surface ofthe light emitting material layer FLR. Accordingly, there exists a largeprobability that the film thickness loss or the step disconnection willbe generated in the counter electrode CT at a portion of the lightemitting material layer FLR where the step disconnection is formed orthe vicinity thereof.

To observe one pixel in the plan structure (see FIG. 3, for example),the step disconnection of the light emitting material layer FLR or thecounter electrode CT which occurs at an extremely limited portion of theend portion of the pixel (for example, a profile of the bank film BNKindicated by a broken line in FIG. 3) (a so-called local stepdisconnection) does not cause any trouble in supplying an electriccurrent to the light emitting material layer FLR (in other words, theimage display operation of the organic EL display device) and hence,such step disconnection can be ignored. However, along with thecontinuation of driving of the organic EL display device (supplying ofan electric current to the light emitting material layer FLR), theelectric current to be supplied to the light emitting material layer FLRis concentrated between the counter electrode CT and the pixel electrodePX which can no more ensure the sufficient spacing due to the stepdisconnection or the film thickness loss of the light emitting materiallayer FLR. When the electric current is locally concentrated on theportion of the light emitting material layer FLR where the stepdisconnection or the film thickness loss is generated (hereinafterreferred to as a defective region of the light emitting material layerFLR), the Joule heat is generated in such a portion and hence, the lightemitting material layer FLR is evaporated around this defective regionthus forming cavities or carbonizing the organic compound whichconstitutes the light emitting material layer FLR.

Further, in the portion of the counter electrode CT where the stepdisconnection or the film thickness loss is generated (hereinafterreferred to as the defective region of the counter electrode CT),moisture, oxygen or the like which is contained in the atmosphere (thatis, remaining in a sealing cap) intrudes into the light emittingmaterial layer FLR through the defective region of the counter electrodeCT. In other words, the defective region of the counter electrode CTconstitutes an inlet which allows the moisture, oxygen or the like tointrude into the light emitting material layer FLR. Accordingly, themoisture, oxygen or the like which intrudes into an extremely limitedregion of the light emitting material layer FLR (the vicinity of the endportion of the pixel) degenerates the light emitting material layer FLRwhich is positioned at the end portion of the pixel whereby thenon-light emitting region is formed. Further, the moisture, oxygen orthe like which intrudes into the light emitting material layer FLRdiffuses into the inside of the light emitting material layer FLR inresponse to the supply of an electricity to the light emitting materiallayer FLR thus spreading the non-light emitting region in the inside ofthe layer.

FIG. 5C shows a cross section of a bank film BNK which is formed oforganic material. FIG. 5C is also an explanatory view of anothercomparison example for the cross section of the bank film BNK of thepresent invention shown in FIG. 5A. Since the organic material layerwhich constitutes the bank film BNK contains the moisture, oxygen or thelike, the moisture, oxygen or the like intrudes into the light emittingmaterial layer FLR which is in contact with the bank film BNK through acontact interface between the light emitting material layer FLR and thebank film BNK and diffuses in the inside of the light emitting materiallayer FLR. Accordingly, compared to the local generation of thenon-light emitting region explained in conjunction with FIG. 5B, in thestructure shown in FIG. 5C which uses the bank film BNK made of theorganic material, the light emitting material layer FLR is degradedalong the above-mentioned contact interface and the non-light emittingregion spreads along the end portion of the pixel.

As can be clearly understood from the above-mentioned two comparisonexamples, in the structure of this embodiment shown in FIG. 5A, (1) byforming the bank film BNK using the inorganic material such as SiNx,SiO₂ or the like, the degradation of the light emitting material layerFLR which is in contact with the bank film BNK can be prevented.

Further, in the structure of this embodiment, (2) to prevent the stepdisconnection or the film thickness loss of the light emitting materiallayer FLR at the end portion of the pixel where the bank film BNK isformed and the step disconnection or the film thickness loss of thecounter electrode CT attributed to the step disconnection or the filmthickness loss of the light emitting material layer FLR, an inclinationangle (taper angle) of the side wall of the bank film BNK with respectto the pixel electrode PX (or a background layer, a principal surface ofa substrate SUB1 as shown in FIG. 1) is limited to a value less than 85degrees. By reference to the planar structure of the pixel shown in FIG.3, the inclination angle of the side wall of the bank film BNK can bealso expressed as an inclination angle with respect to the pixelelectrode PX (conductive layer) of the side wall of the opening portionfor exposing the pixel electrode PX.

Here, by forming the bank film BNK using the inorganic material layer,it is possible to decrease a film thickness “t” of the bank film BNK andhence, an advantageous effect that a stray light (smear) to the pixelregion from other pixel region which is arranged close to the pixelregion can be also reduced.

Here, when the bank film BNK is formed of the organic material layer, afilm thickness of the bank film BNK becomes approximately 1 μm and thisgives rise to a drawback such as lowering of contrast due to the straylight (smear).

To consider the film thickness “t” of the bank film BNK which is formedof the inorganic material layer, assuming a film thickness of the lightemitting material layer FLR as “t1” and a film thickness of the counterelectrode CT as “t2”, the relationship to t ≈t1+t2 is established. It ispreferable to establish the relationship to t<t1+t2. Further, it issuitable to ensure at least the relationship ½t<t1+t2. By forming thebank film BNK using the inorganic material layer, it is possible to setthe film thickness of the bank film BNK in the above-mentioned manner.

<<Manufacturing Method>>

FIG. 6 is a view showing one embodiment of a manufacturing method of thebank film BNK.

The pixel electrodes PX (not shown in the drawing) are formed on thesurface of the substrate SUB1 made of glass and, thereafter, a siliconnitride film (SiNx), for example, is formed on the surface of thesubstrate SUB1. In this case, the silicon nitride film has thethree-layered structure which is constituted of different layers, forexample. That is, the silicon nitride film is sequentially formed suchthat a silicon nitride film having a low etching rate which constitutesa first layer, a silicon nitride film having an intermediate etchingrate which constitutes a second layer, and a silicon nitride film havinga fast etching rate which constitutes a third layer are sequentiallyformed in order from the substrate SUB1 side.

In an example in which the bank film BNK formed of the silicon nitridefilm having the three-layered structure using a plasma enhanced CVDmethod, a ratio (flow rate) of a monosilane gas and an ammonium gaswhich are supplied to a CVD chamber (film forming chamber) is controlledso as to sequentially reduce a ratio of nitrogen (N) which is containedin respective gases in order from the silicon nitride film whichconstitutes the first layer (principal surface side of the substrateSUB1) toward the silicon nitride film which constitutes the third layer(the light emitting material layer FLR and the counter electrode CTbeing formed on an upper surface thereof). Further, the third layer maybe formed of a silicon film in which impurities are not intentionallyincluded in place of the silicon nitride film. Further, the bank filmBNK may be formed of a two-layered silicon nitride film. Further, anitrogen content of at least one silicon nitride films included in thebank film may be lowered than a silicon content of nitride silicon whichsatisfies stoichiometric ratio (also expressed as Si₃N₄, . . . SiN_(x)(x=1.33). For example, even when the bank film BNK (having the structurein which the bank film BNK is formed by laminating silicon nitride filmsin two layers) is formed of a first silicon nitride film which is formedon the principal surface side of the substrate SUB1 and has thecomposition of SiN_(1.3) and a second silicon nitride film which isformed on the first silicon nitride film with a thickness smaller than athickness of the first silicon nitride film and has the composition ofSiN_(0.9), a side wall of the bank wall BNK is inclined with an angle ofless than 85 degrees.

Then, by selectively etching such a laminated film by a photolithographytechnique, it is possible to form the inclination which flares towardthe substrate SUB1 side in the side wall of the opening portion.Further, an angle of inclination (less than 85 degrees) can be obtainedby changing the composition of an etchant, for example.

Embodiment 2

FIG. 7A to FIG. 7C are cross-sectional views respectively showinganother embodiments of the side wall of the opening portion of the bankfilm BNK.

In providing the inclination of less than 85 degrees with respect to theprincipal surface of the substrate SUB1 (or the upper surface of thepixel electrode PX which is in contact with the bank film BNK as shownin FIG. 1 and FIG. 4) to the opening portion of the bank film BNK, dueto conditions of wet etching or the dry etching, there may be a casethat the side wall of the bank film BNK makes an angle of 85 degrees ormore with respect to the principal surface of the substrate SUB1. In allof FIG. 7A to FIG. 7C, the side wall of the bank film BNK makes an angleof 85 degrees or more with respect to the principal surface of thesubstrate SUB1 in a region close to an tipper surface of the bank filmBNK. Further, in FIG. 7C, the side wall of the bank film BNK bendsbackward toward the opening of the bank film BNK by making an angleclose to 100 degrees with respect to the principal surface of thesubstrate SUB1. However, in all of the side walls of the bank films BNKshown in FIG. 7A to FIG. 7C, between one end of the side wall which isin contact with the principal surface of the substrate SUB1 and anotherend of the side wall which is close to the upper surface of the bankfilm BNK, there exists a region where the side wall makes an angle ofless than 85 degrees with respect to the principal surface of thesubstrate SUB1.

In this manner, even when only a portion of the side wall of the bankfilm BNK makes an angle of less than 85 degrees with respect to theprincipal surface of the substrate SUB1, it is possible to suppress theprobability that the light emitting material layer (organic materiallayer) FLR and the counter electrode (cathode layer) CT which are formed(stacked) on the bank film BNK are disconnected at the stepped portionbetween the principal surface of the substrate SUB1 (upper surface ofthe pixel electrode PX) and the upper surface of the bank film BNK. Whenthe above-mentioned light emitting material layer is formed of amulti-layered film formed of a plurality of organic materials (forexample, an electroluminescent material layer and an electron injectinglayer and a hole injecting layer which sandwich the electroluminescentmaterial layer), it is preferable to set a region where the side wall ofthe bank film BNK and the principal surface of the substrate SUB1 (uppersurface of the pixel electrode PX) make an angle of less than 85 degreesbetween the principal surface of the substrate SUB1 (upper surface ofthe pixel electrode) and the upper surface of the bank film BNK to ahalf or more of the side wall. In other words, with respect to the sidewall rising from the principal surface of the substrate SUB1 to theupper surface of the bank film BNK, it is not necessary to provide anangle which makes less than 85 degrees with respect to the principalsurface of the substrate SUB1 to the side wall of the bank film BNKuniformly and it is allowable to partially provide an angle which makes85 degrees or more with respect to the principal surface of thesubstrate SUB1 to the side wall.

Accordingly, as shown in FIG. 7A to FIG. 7C respectively, steep inclinedsurfaces having an angle of approximately 90 degrees or an angle of 90degrees or more may be partially provided to the side wall from the endportion of the side wall at the substrate SUB1 side to the surface ofthe bank film BNK. This is because that these steep inclined surfaceshave a relatively small height (a ratio with respect to a distance fromthe principal surface of the substrate SUB1 to the upper surface of thebank film BNK) and hence, the probability that the step disconnectionoccurs in the conductive layer applied to the portion is extremelysmall.

That is, it is sufficient that the a portion of the side wall from theend portion of the side Wall at the substrate SUB1 side to the surfaceof the bank film BNK has an inclination angle of less than 85 degrees.

Embodiment 3

FIG. 8A to FIG. 8D are cross-sectional views respectively showinganother embodiments of the side wall of the opening portion of the bankfilm BNK.

Since the inclined surface of the side wall of the opening portion ofthe bank film BNK is formed by making use of the difference in theetching rate among respective layers of the bank film BNK as describedabove, it is a rare case that the side wall is formed as a straight flatface and it is often a case that the side wall is formed in a curvedshape as shown in FIG. 8A to FIG. 8D. In FIG. 8A and FIG. 8D, a portionof the side face of the bank film BNK which is in contact with theprincipal surface of the substrate SUB1 (or a tangent or a contact flatface which is in contact with the portion) makes an angle of 85 degreesor more with respect to the principal surface of the substrate SUB1. InFIG. 8B and FIG. 8D, a portion of the side face of the bank film BNK inthe vicinity of the upper surface of the bank film BNK (or a tangent ora contact flat face which is in contact with the portion) makes an angleof 85 degrees or more with respect to the principal surface of thesubstrate SUB1. In FIG. 8C, a center portion of the side face of thebank film BNK (or a tangent or a contact flat face which is in contactwith the portion) makes an angle of 85 degrees or more with respect tothe principal surface of the substrate SUB1.

Also in these cases, so long as the side face of the bank film BNK hasan inclined surface of less than 85 degrees at a portion thereof fromthe end portion of the side wall at the substrate SUB1 side to thesurface of the bank film BNK (the upper surface covered with anelectrode CT and the like), it is possible to suppress the degradationof a light emitting material layer FLR and the rupture of a thin filmsuch as the electrode CT or the like which is stacked in a stridingmanner over a stepped portion between the principal surface of thesubstrate SUB1 and the upper surface of the bank film BNK.

Here, in the above-mentioned respective embodiments, although thecounter electrode CT is formed of the non-light transmitting conductivelayer made of aluminum or the like, it is needless to say that thecounter electrode CT may be formed of a light transmitting conductivefilm such as an ITO film and light from the light emitting materiallayer FLR is taken out from the counter electrode CT side. In this case,the pixel electrode PX may be formed of a non-light transmittingconductive layer.

As can be clearly understood from the foregoing explanation, accordingto the organic EL display device of the present invention, it ispossible to suppress the step disconnection of the counter electrode.

1. An organic EL display device comprising: a substrate; a plurality ofpixel regions each of which has at least a first electrode, a lightemitting material layer, and a second electrode laminated in this orderabove a principal surface of the substrate, wherein the plurality ofpixel regions are arranged two-dimensionally in the principal surface ofthe substrate; and a bank film formed above the principal surface of thesubstrate to separate respective ones of the plurality of pixel regionsfrom others of the plurality of pixel regions adjacent to the respectiveones of the plurality of pixel regions, wherein the bank film hasopenings each of which exposes the first electrode provided for therespective ones of the plurality of pixel regions, wherein the lightemitting material layer is formed in the opening of the bank film to beextended to a side wall of the bank film lying along the opening in therespective ones of the plurality of pixel regions, wherein the secondelectrode provided for the respective ones of the plurality of pixelregions is formed in common with that provided for the others of theplurality of pixel regions adjacent to the respective ones or theplurality of pixel regions, and wherein the bank film is comprised of atleast one inorganic material, has the side wall thereof sloped at anangle less than 85 degrees with respect to the principal surface of thesubstrate, and is comprised of a plurality of layers, the compositionratio of the plurality of layers being different from one another. 2.The organic EL display device according to claim 1, wherein the sidewall of the bank film is shaped into a curvature extended from an uppersurface of the first electrode to an upper surface of the bank film. 3.The organic EL display device according to claim 1, wherein the sidewall of the bank film is partially sloped at an angle not less than 85degrees with respect to the principal surface of the substrate betweenan upper surface of the first electrode to an upper surface of the bankfilm.
 4. An organic EL display device comprising: a substrate; and aplurality of pixel regions arranged in a principal surface of thesubstrate, respective ones of plurality of pixel regions having a firstelectrode, a bank film, a light emitting material layer, and a secondelectrode stacked in this order above the principal surface of thesubstrate, wherein the bank film spaces the first electrode provided forthe respective ones of the plurality of pixel regions from the firstelectrodes provided for others of the plurality of pixels regionsadjacent to the respective ones of the plurality of pixel regions,wherein the second electrode is formed in common with the plurality ofpixel regions, wherein the bank film has an opening exposing a part ofan upper surface of the first electrode toward the light emittingmaterial layer and a side wall located along the opening, wherein thelight emitting material layer is formed in the opening the bank film andin the vicinity thereof, and wherein the bank film is comprised of atleast one inorganic material, has the side wall thereof sloped at anangle less than 85 degrees with respect to the principal surface of thesubstrate, and is comprised of a plurality of layers, the compositionratio of the plurality of layers being different from one another. 5.The organic EL display device according to claim 4, wherein the sidewall of the bank film is shaped into a curvature extended from an uppersurface of the first electrode to an upper surface of the bank film. 6.The organic EL display device according to claim 4, wherein the sidewall of the bank film is partially sloped at an angle not less than 85degrees with respect to the principal surface of the substrate betweenan upper surface of the first electrode to an upper surface of the bankfilm.